LED lights are more energy-saving and more environment-friendly as compared with traditional fluorescent or incandescent lights, and thus LED lights gradually replace the existing fluorescent or incandescent lights. For incandescent light with a TRIAC dimmer, it also intends to be replaced by a LED lights, and thus LEDs need to be compatible with the TRIAC dimmer. However, when LED lights are used to replace incandescent lights, since the output terminal voltage of the TRIAC will have great voltage change rate (dv/dt) when it is turned on, great surge current will be generated at the input terminal. The surge current has great shock amplitudes and small duration time, which is easy to cause the TRIAC to be turned off, thus affecting the stable work of the LED driving circuit and making the LED lights flicker; in addition, the input current of the TRIAC device needs to be greater than its holding current; when the input current is smaller than the holding current, it is easy to make the TRIAC to be turned off, which will also cause flickering of LED. In order to solve the above technical problems, the prior art uses the following solutions, which still have some technical defects.
FIG. 1 shows a prior art passive bleeder solution, which uses an RC as the passive bleeder components. This solution has a simple structure and low cost. However, at the end of the power frequency cycle, it cannot provide the current required to keep the TRIAC to turn on. Since capacitor C00 is charged to yin or close to yin after the TRIAC is turned on, and then it is discharged through resistor R00. Since the time constant of RC is large, it may even discharge at the middle or tail of the half period, which reduces the input current instead, and this is not good for the stable turning-on of the TRIAC.
FIG. 2 shows a prior art active bleeder circuit. The input current is sampled by a resistor R02, and the bleeder current iblr is controlled to make the input current not smaller than VREF0/R02, to ensure the turning-on of the TRIAC. This solution may compensate for the input current in an all-input scope, and overcome the defect in the RC solution that it cannot provide current at the tail end. Since it needs to ensure that the input current is not smaller than VREF0/R02 all the time, the solution has the defects of low efficiency and high temperature rising, and it will have an adverse effect on the reliability of the system and increase cost.